A comparative study of PffBT4T-2OD/EH-IDTBR and PffBT4T-2OD/PC71BM organic photovoltaic heterojunctions

In order to clarify the different photovoltaic performance and “burn-in” degradation mechanism, the electron donor poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′;5′,2″;5″,2′″-quaterthiophen-5,5′″-diyl)] (PffBT4T-2OD), fullerene derivative acceptor [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) and the nonfullerene acceptor indacenodithiophene core flanked with benzothiadiazole and rhodanine groups with the branched (2-ethylhexyl) chains (coded as EH-IDTBR) were selected to construct PffBT4T-2OD/EH-IDTBR and PffBT4T-2OD/PC71BM complexes as heterojunction interface models. The geometries, electronic structures, excitation properties and the rates of electron processes were extensively explored based upon quantum chemistry calculations. The results indicate that the light harvesting capability of EH-IDTBR is far better than that of PC71BM. Most of excited states of PffBT4T-2OD and EH-IDTBR exhibit intramolecular charge transfer characters. Compared with PffBT4T-2OD/PC71BM, the better planarity, stronger non-bonding interactions, and the hybrid excited states, as well as the larger electrostatic potential difference between the donor and acceptor of PffBT4T-2OD/EH-IDTBR are responsible for its better photovoltaic performance and the lower “burn-in” degradation. Although the rates of charge recombination of PffBT4T-2OD/EH-IDTBR complex is larger, its faster rates of exciton dissociation and charge transfer processes can be helpful to resist “burn-in” degradation. The results are helpful to develop novel OPV materials that are resistant to “burn-in” degradation.